1. Field Of The Invention
This invention relates to a delay stopper for use in mine roof anchors wherein a roof bolt is threaded into a threaded member and the roof bolt and the threaded member rotate as a unit in order to mix resin that at least partially secures the mine roof anchor within a bore hole formed in the mine roof. The invention also relates to a method of manufacturing the delay stopper.
2. Description Of The Prior Art
It is well-known in the art of mine roof support to tension bolts anchored in bore holes drilled in the mine roof to reinforce the unsupported rock formation above the roof. Conventionally, a bore hole is drilled through the roof into the rock formation. The end of the bolt in the rock formation is anchored by either engagement of an expansion shell on the end of the bolt with the rock formation, or adhesively bonding the bolt by a resin to the rock formation, or by utilizing a combination of an expansion shell and resin bonding to secure the roof anchor within the bore hole.
U.S. Pat. Nos. 3,877,235, 4,051,683, and 4,477,209 all disclose the adhesive bonding of an element of a mine roof anchor within a bore hole. Each of these patents shows some form of delay mechanism to permit the roof bolt and the portion to be bonded to rotate as a unit while the resin is being mixed.
U.S. Pat. Nos. 4,413,930, 4,419,805, 4,516,885, 4,518,292, and 4,611,954 all disclose mine roof anchors in which an expansion shell and resin bonding are utilized in combination to anchor the mine roof anchor within the bore hole formed in the mine roof. These patents also disclose a delay mechanism utilized to prevent relative rotation of the mine roof bolt and the expansion shell while the resin components are being mixed.
U.S. Pat. Nos. 3,940,941, 3,979,918, 4,295,761, British Patent No. 2,067,702, Australian Patent Abstract AV-A1-68 116/81 and Australian Patent Abstract AU-A-78 424/81 all disclose forms of threaded members securable to the ends of mine roof anchors adjacent the mine roof to tension the roof anchor after it has been secured within the bore hole formed in the roof. The threaded members have delay mechanisms which break away when a predetermined torque is exceeded.
While each of the foregoing patents discloses a delay means to permit the mixing of the resin during rotation of the shaft of a mine roof bolt and the anchoring mechanism as a unit and thereafter to provide for tensioning of the mine roof bolt after the anchoring unit has been fixed to the bore hole, there is still a need for an improved delay stopper for such roof anchors that provides consistent delay, is readily manufactured, and is economical to manufacture.